The present invention relates to improved electrolytic cells utilized for the decomposition of aqueous salt solutions. A number of industrial processes are based upon the electrolysis of such solutions. Among the most important is the electrolysis of alkali metal chlorides to produce chlorine and either the corresponding alkali metal hydroxide, or chlorate. Of the alkali metal chloride source materials, sodium chloride is the most abundant and most utilized.
The electrolysis process is commonly carried out in an electrolytic cell which consists of a cell compartment containing a plurality of spaced anodes and cathodes separated by a porous diaphragm or separator. For some years, a layer of fibrous asbestos was utilized as the diaphragm. More recently, with the advent of metal, or dimensionally stable anodes, perm selective separators, such as fluorocarbon resin modified abestos mixtures, have substantially replaced the sole use of abestos as the diaphragm component.
The spacing between the anode and the cathode is economically important as the amount of electrolyte that fills the space, or gap, has an electrical resistance requiring additional electrical energy to operate the cell. The additional energy used results in a temperature increase in the electrolyte which ultimately limits the current density at which the cell may be operated.
If the gap could be arbitrarily selected it would be chosen to maintain the cell voltage as close as possible to the decomposition voltage of the electrolyte. Thus a narrow, but discrete, space between the electrodes is highly desirable. However, because of the broad areas of anode and cathode that require spacing, the desired spacing is difficult to obtain and to subsequently maintain. In addition, in the assembly of an electrolytic cell, it is important to provide a means of guiding the electrodes into the cell compartment without damaging the coated surface of the anode and to avoid disrupting the diaphragm. Generally inter-electrode distances presently in the range from about 1/32 to about 1/4 inch, and more preferably from about 1/16 to about 1/8 inches.
Various methods and techniques have been proposed to place the electrodes into the desired spaced relation and to maintain them in such relation during operation of the cell. For example, U.S. Pat. No. 3,247,090 teaches the use of metal spacers attached to the cathodes; U.S. Pat. No. 3,477,939 teaches the use of spacer blocks attached to the anode; U.S. Pat. No. 3,732,153 teaches plastic cords wrapped around the cathode, and; U.S. Pat. No. 3,975,255 describes the use of non-conductive spacers positioned on the anode edges.